Coordinate position measuring by imaging a movable grating onto a parallel reference grating

ABSTRACT

In order to position a slide relative to two coordinate directions, two gratings are used, the rules thereon being parallel to each other and non-parallel to neither of the coordinate directions and in which one of the gratings is integral with said slide. The rules on the one grating are opaque whereas those on the other grating are transparent. When the rules of the gratings coincide in the course of imaging the gratings on each other, signals will be derived at subsequent photocells.

United States Patent [191 Grey et al.

[451 Feb. 12, 1974 COORDINATE POSITION MEASURING BY IMAGING A MOVABLEGRATING ONTO A PARALLEL REFERENCE GRATING [75] Inventors: Udo Grey;Winfried Klimmer, both of Jena-Neulobeda, Germany [73] Assignee:Jenoptik Jena G.m.b.H., Jena,

Germany [22] Filed: Mar. 6, 1973 [21 Appl. No.: 337,359

[52] US. Cl 356/169, 356/170, 250/237 R [51] Int. Cl. G01b 11/14 [58]Field of Search... 356/156, 169, 170, 171, 172;

[56] References Cited UNITED STATES PATENTS 3,723,748 3/1973 Coburn etal 250/237 G Wogatzke 250/237 R Weyrauch 356/169 X PrimaryExaminerRonald L. Wibert Assistant ExaminerPaul K. Godwin 5 7 ABSTRACTIn order to position a slide relative to two coordinate directions, twogratings are used, the rules thereon being parallel to each other andnon-parallel to neither of the coordinate directions and in which one ofthe gratings is integral with said slide.

The rules on the one grating are opaque whereas those on the othergrating are transparent.

When the rules of the gratings coincide in the course of imaging thegratings on each other, signals will be derived at subsequentphotocells.

4 Claims, 2 Drawing Figures 1 COORDINATE POSITION MEASURING BY IMAGING AMOVABLE GRATING ONTO A PARALLEL REFERENCE GRATING This invention isconcerned with a device for positioning slides in at least onecoordinate direction, particularly for precision measuring apparatus andcoordinate measuring systems. Such a device may be utilized, for examplein industries concerned with semiconductors.

In a known coordinate measuring system for measuring the relativeCartesian coordinates of points in, on or along an object, a transportcarries two measuring gratings, the rules on which being associated toand stand perpendicular on the respective coordinates, wherein the ruleson one grating being at right angles to the rules on the other grating.The device further includes an object support which may be preciselyadjusted by movements of a transport into a predetermined position, themeasuring point of which is defined by the rules on the measuringgratings relative to the coordinate system.

Each measuring grating is associated to a reference grating, the ruleson which are parallel to those of the associated measuringgrating.

Each measuring grating and associated reference grating include anillumination optical system, an imaging optical system andlight-sensitive elements.

Such a device is disadvantageous because each coordinate directionrequires a measuring grating, a reference grating, an imaging andillumination optical system, and light-sensitive elements of its own.

Furthermore, unduly high adjustment efforts are involved to have thegratings in register with the respective coordinate direction, sinceprecision instruments in particular require an accurate angularalignment of the gratings.

Another known device for automatically positioning cross-slides relativeto two coordinate directions employs one measuring grating for eachcoordinate direction, comprising illumination, imaging and scanningmeans, y

In order to position the slide in the coordinate directions, theassociated measuring grating is scanned through a reticle diaphragm.

The essential drawback of such a device results from the two requiredmeasuring gratings, which have to be produced with high precision andwhich have to be adjusted relative to the coordinate directions.

However, the use of a reticle diaphragm involves additional interferencepulses in the course of the positioning operation, which will move thestage to erroneous positions.

With a known optical measuring device, at least one oscillatingluminescent light spot is visually or optoelectronically indicative ofthe position of an object.

The oscillating light spot is projected onto the plane of a reflector,mounted on a-stage and provided with crossing lines, which are inclinedrelative to the .direction of displacement.

One set of lines on the reflector is associated to a respectivedirection of displacement.

Two crossing marks located in special adjustment rings are angularly andcrossingly adjustable relative to each other, thus forming the scanningmarks.

By the use of scanning marks which are crossing each other interferencepulses arrive at the opto-electronical detectors. Furthermore, theproduction of reflectors bly simplified by an advantageous embodimentand in- -terference pulses responsible for erroneous optoelectronicaldetection, are eliminated, and a high positioning precision may. beobtained.

Accordingly, the present invention is concerned with a device forpositioning a slide in at least one coordinate direction including ameasuring grating, representing the scale and being integral with theslide to be positioned, said measuring grating being illuminated bymeans of an illumination optical system, and being imaged by means of animaging optical system onto a slit diaphragm, and the images of saidmeasuring grating and said slit diaphragm being in turn projected ontoopto-electronical detectors, characterized in that said measuringgrating and said slit-diaphragm are arranged in such a manner that theparallel rules on said measuring'grating and the slits of said slitdiaphragm include an angle of 45 relative to the direction ofdisplacement of the slide.

The device of the present invention considerably simplifies theproduction of the measuring grating and the adjustment thereof relativeto the slide.

Only an angular orientation of one grating relative to the coordinatedirection of the slide has to be carried out.

Furthermore, only one illumination light source, and respective opticalsystem, and one imaging optical system are required for positioning theslides in at least one coordinate direction. Interference pulses areeliminated at the subsequent opto-electronical detectors by utilizing aslit diaphragm, exhibiting no crossing lines or crossing slits, thusavoiding inaccurate results in the course of the positioning operation.

In order that the invention may be more readily understood, reference ismade to the accompanying drawings which illustrate diagrammatically andby way of example one embodiment thereof, and in which FIG. 1 is aschematic perspective view of a cross slide positioning device, and

FIG. 2 an enlarged schematic view of the rules on a measuring gratingand of a slit diaphragm.

A device for positioning a displaceable cross-slide 1 along twocoordinate directions x and y comprises a measuring grating 2, an object12, both mounted on the cross-slide 1, an illumination system, includinga light source 3 and an illumination optical system 4, and an imagingoptical system 5 adapted to image opaque rules 6 of the measuringgrating 2 in the plane of a slit diaphragm 7 (reference grating). Theslit-diaphragm 7 (reference grating) is disk-shaped and is provided withtransparent rules 8.

The measuring grating 2 and the slit diaphragm 7 are arranged relativeto the two coordinate directions x and y (FIG. 1) in such a manner thatthe rules 6 of the measuring grating 2 and the slits 8 of the slitdiaphragm 7 on the one hand, and the coordinate directions on the otherhand include an angle of 45.

Preferably, a second imaging optical system is inserted into the path ofrays of the positioning device, in order to project the slit-diaphragm 7(reference grating) and the image of the measuring grating 2 onto atleast one opto-electronical detector 9.

In FIG. 2 the position of the rules 6 in the plane of the slit diaphragm7 (reference grating) and the position of the'transparent rules 8 of theslit diaphragm 7 (reference grating) are shown on an enlarged scale. Thespaces designated by Ax and Ay between the transparent rules 8 in the xand y directions are equal and are indicative of the measurable way ofdisplacement. Such an arrangement of the rules 6 on the grating and thetransparent rules 8 permits the use of only one measuring grating 2 andone slit diaphragm 7 (reference grating) to ensure a precise positioningof the crossslides in the x direction as well as in the y direction. Theelectrical signals derived from the detectors 9 are fed into a signalprocessing means 11 for subsequent processing.

The device according to the invention is not restricted to embodimentsin which the measurable way of displacements designated by Ax and Ay areidentical. Ax and Ay may well assume different values, in other words,the rules 6 on the measuring grating 2 and the rules 8 on the slitdiaphragm 7 (reference grating) may include an angle unlike 45 relativeto the coordinate directions. Furthermore, the slit diaphragm 7(reference grating) and the measuring grating 2 are mutuallyexchangeable. If required, the device permits an operation without theoptical imaging systems 5 and- 10.

With a further advantageous embodiment, the slide 1 may benon-displaceable, whereas the system constituted by the illuminationsystem 3, 4 the imaging optical system 5, 10, the slit diaphragm 7(reference grating) and the light-sensitive means 9 may be displaceablyarranged.

We claim:

1. A device for positioning an object relative to at least twocoordinate directions comprising a slide for carrying said object,

a measuring grating having rules thereon being inclinedly orientedrelative to said coordinate directions,

a reference grating, being arranged in a plane and being parallel andoptionally conjugated to the plane of said measuring grating, and havingrules thereon, oriented in-parallel to the rules on said measuringgrating, the one of the gratings having opaque rules, the other of thegratings having transparent rules, one of said gratings beingnon-displaceably secured to said slide,

an illumination system adapted to illuminate one of said gratings,

at least one light-sensitive means said gratings being located betweensaid illumination system and said light-sensitive means, said opticalillumination system, said gratings and said light sensitive means beingin optical alignment to each other; 1 the grating integral with saidslide being jointly displaceable relative to the other grating, to saidillumination system and to said light sensitive means in direction ofboth coordinates, and finally comprising signal processing means adaptedto process signals derived from said light sensitive means.

2. A device as claimed in claim 1, wherein said rules. 'and saidcoordinate directions include an angle of 45.

means.

1. A device for positioning an object relative to at least twocoordinate directions comprising a slide for carrying said object, ameasuring grating having rules thereon being inclinedly orientedrelative to said coordinate directions, a reference grating, beingarranged in a plane and being parallel and optionally conjugated to theplane of said measuring grating, and having rules thereon, oriented inparallel to the rules on said measuring grating, the one of the gratingshaving opaque rules, the other of the gratings having transparent rules,one of said gratings being non-displaceably secured to said slide, anillumination system adapted to illuminate one of said gratings, at leastone light-sensitive means said gratings being located between saidillumination system and said light-sensitive means, said opticalillumination system, said gratings and said light sensitive means beingin optical alignment to each other; the grating integral with said slidebeing jointly displaceable relative to the other grating, to saidillumination system and to said light sensitive means in direction ofboth coordinates, and finally comprising signal processing means adaptedto process signals derived from said light sensitive means.
 2. A deviceas claimed in claim 1, wherein said rules and said coordinate directionsinclude an angle of 45*.
 3. A device as claimed in claim 1, furthercomprising a first optical imaging system adapted to image said gratingson each other and being arranged between said gratings.
 4. A device asclaimed in claim 3, still further comprising a second optical imagingsystem for at least partially imaging the two gratings onto said lightsensitive means, said second optical imaging system being arrangedbetween the two gratings and said light sensitive means.